A hydraulic construction machine such as a hydraulic excavator, generally, includes a diesel engine as a prime mover and carries out necessary work by rotatively driving at least one variable displacement hydraulic pump by the engine and driving hydraulic actuators by a hydraulic fluid delivered from the hydraulic pump. The diesel engine is provided with input means such as an accelerator lever for instructing a target revolution speed, and an amount of injected fuel is controlled depending on the target revolution speed, whereby the revolution speed is controlled.
With respect to control of an engine and a hydraulic pump in such a hydraulic construction machine, JP, A, 62-8618, entitled "Control Method for Driving System Including Internal Combustion Engine and Hydraulic Pump", proposes one control method. The proposed control method is an example of the so-called speed sensing control with which a difference between the target revolution speed and the actual engine revolution speed (i.e., a revolution speed deviation) is determined by a revolution speed sensor, and an input torque of the hydraulic pump is controlled using the revolution speed deviation.
The purpose of that control is to reduce the load torque (input torque) of the hydraulic pump and to prevent the engine from stalling, thereby enabling the engine output power to be effectively utilized, when the detected actual engine revolution speed is reduced relative to the target revolution speed.